Key performance features required in a golf ball include distance, controllability, durability and feel at impact. Balls endowed with these qualities in the highest degree are constantly being sought. A succession of golf balls having multilayer constructions typically composed of three layers have emerged in recent years. By providing golf balls with a multilayer construction, it has become possible to combine numerous materials of different properties, enabling a wide variety of ball designs in which each layer has a particular function.
Of these, functional multi-piece solid golf balls having an optimized hardness relationship among the layers encasing the core, such as an intermediate layer and a cover (outermost layer), are widely used. For example, golf balls which have three or more layers, including at least a core, an intermediate layer and a cover, and which are focused on design attributes such as the core diameter, the intermediate layer and cover thicknesses, the deflection of the core under specific loading and the hardnesses of the respective layers, are disclosed in the following patent publications: JP-A H11-151320, JP-A 2003-190331, JP-A 2006-289065, JP-A 2011-115593, JP-A H8-336617, JP-A 2006-230661, JP-A 2017-46930, JP-A 2017-86579, JP-A 2009-95358, JP-A 2016-101256, JP-A 2013-150770, JP-A 2013-150771, JP-A 2012-139337, JP-A 2012-80923, JP-A 2012-139401, JP-A 2012-223286, JP-A H11-206920, JP-A 2014-110940, JP-A 2011-172930, JP-A 2002-325863 and JP-A 2017-113308.
In the golf balls of JP-A H11-151320, JP-A 2003-190331, JP-A 2006-289065, JP-A 2011-115593, JP-A H8-336617, JP-A 2006-230661, JP-A 2017-46930, JP-A 2017-86579, JP-A 2009-95358 and JP-A 2016-101256, the core is formed as a two-layer core, but these two-layer cores lack optimized hardness profiles, leaving room for improvement. In the golf balls of JP-A 2013-150770, JP-A 2013-150771, JP-A 2012-139337, JP-A 2012-80923, JP-A 2012-139401 and JP-A 2012-223286, the core is formed as a two-layer core, but the inner core layer in these two-layer cores has a small diameter. The golf ball of JP-A H11-206920 is a three-piece solid golf ball in which a two-layer core is encased by one cover layer; that is, the cover consists of a single layer. Finally, in the golf balls of JP-A 2014-110940, JP-A 2011-172930, JP-A 2002-325863 and JP-A 2017-113308, the core is formed as a two-layer core, but the hardness profile of the two-layer core in each of these disclosures is not optimized. From the standpoint of achieving a greater flight performance and imparting higher controllability on approach shots, there remains room for improvement in the construction of these prior-art golf balls.